The purpose of this project is to conduct systematic parametric studies of nicotine replacement therapy using nicotine polacrilex gum. Proposed studies to be conducted within the context of a behaviorally oriented stop smoking treatment clinic will manipulate treatment parameters in order to identify variables that influence outcome. Experiment 1 will determine dose-effects of nicotine replacement therapy (7 versus 15 pieces per day of 2 mg gum) in a placebo controlled random assignment protocol with attention to relapse, withdrawal and weight gain outcomes. This study should provide important information about optimal dosing levels in relation to individual pre-cessation levels of nicotine exposure. Experiment 2 will examine the transition between smoking and nicotine replacement therapy (abrupt cessation versus prior cutdown) in order to characterize the influence of experimentally determined pre-cessation nicotine exposure levels on post-cessation treatment outcomes. Experiment 3 will examine nicotine replacement therapy duration (0,3,6 and 12 weeks of treatment with active gum) in order to determine whether there are any demonstrable clinical benefits associated with longer versus shorter duration regimens. Overall, these studies should provide important information about the factors that influence the clinical outcome of nicotine replacement therapy. Data obtained through parametric manipulation of treatment parameters will be useful for establishing optimal clinical intervention strategies and the studies should add to our understanding of the mechanisms of action of nicotine replacement therapy.